New York City’s ports, the busiest on the East Coast, ground to halt after an “apparent labor walk off,” according to an e-mailed alert Friday from the Port Authority of New York and New Jersey. “All efforts to resume activity will be undertaken,” the e-mailed alert said. Steve Coleman, a spokesman for the Port Authority, wasn’t immediately available for comment. Beverly Fedorko, a spokeswoman for the New York Shipping Association, which represents the terminal operators, ocean carriers, stevedores said the it was “trying to understand the reason for what appears to be a walkout and will take every measure available to ensure work resumes.” While known for its airports, bridges and Times Square bus terminal, the Port Authority runs the busiest port on on the eastern seaboard. More than 3 million containers are unloaded at its six terminals each year, serving 23 million customers.